Tooling system for thermoforming and trimming a heated sheet of material to form a molded part

ABSTRACT

An upper press platen supports an upper mold member slidable vertically within a surrounding upper trim frame. A lower press platen supports a lower trim frame surrounding a lower mold member slidable vertically within the lower trim frame. The lower mold member defines a cavity connected to a vacuum source, and one or two heated sheets of material are positioned between the trim frames and mold members which are then closed to clamp peripheral portions of the sheets between the trim frames. The lower heated sheet is vacuum formed into the cavity and the sheets are fused together with heat and pressure to form a part which is then cooled. The mold members shift downwardly as a unit within the trim frames to shear the peripheral portions of the sheets from the part. The trimmed part and peripheral portions are removed after the trim frames and mold members open.

RELATED APPLICATION

This application is a division of application Ser. No. 12/387,104, filedApr. 28, 2009.

BACKGROUND OF THE INVENTION

In a thermoform tooling system for producing a vacuum-formed part, suchas, for example, a twin-sheet thermoformed pallet as disclosed in U.S.Pat. No. 5,813,355, it is known to use a thermoforming method andapparatus such as disclosed in U.S. Pat. No. 5,843,366, the disclosureof which is herein incorporated by reference. Other forms ofthermoforming apparatus and methods for producing a twin-sheet orsingle-sheet molded product or part are disclosed in U.S. Pat. No.5,980,231, U.S. Pat. No. 6,379,606 and U.S. Pat. No. 7,045,086. Asdisclosed in U.S. Pat. No. 5,843,366, a pair of heat deformable orthermoplastic sheets each have peripheral edge portions gripped by atransfer clamping frame supported by rotary transfer wheel. The sheetsand frames are indexed through an oven for heating the sheets to apredetermined temperature, for example, 400 degrees F. The heated sheetsare then transferred to a vacuum molding apparatus where upper moldmembers or male molds are supported by a vertically movable upper platenand cooperate with a lower mold member or female mold and another malemold or plug mold which shift horizontally on a lower press platen topositions under the upper male molds.

After the first heated sheet is thermoformed, its clamping frame isreleased, and the empty frame cycles out of the way. The second clampingframe with a heated sheet cycles in and is thermoformed and thenpositioned above or below the first thermoformed sheet. The male andfemale molds are then closed to fuse the upper sheet to the lower sheetto form a twin-sheet plastic pallet or part. After the twin-sheets arefused together, the mold opens, and the combined twin-sheets aretransferred by a single clamping frame to a station where the fusedsheets are cooled. The sheets are then transferred to an unloadingstation where the single clamping frame is opened to release the fusedtwin-sheets forming the part. The combined twin-sheets and the connectedperipheral edge portions, commonly referred to as offal, are manuallytransferred to a trimming station where the peripheral edge portions oroffal are removed or cut from the part with a hand held router or by asteel trim die in a press or by a computer numerically controlled (CNC)router which moves around the molded part.

It has been found that the trimming operation of a thermoformed part,such as the twin-sheet thermoformed pallet, requires substantial timeand labor, in addition to fixtures and equipment for trimming theperipheral portion or offal from the part and to obtain a precisionfinished outer edge on the part. For example, the use of a CNC routerrequires an additional mold or fixture to hold the part securely in itsformed shape. The part is held in place by either manually clamping thepart to a fixture or by a vacuum which requires that the base of thefixture be constructed to allow the fixture to be connected to a vacuumpump in order to hold the part securely. When a steel trim die is used,the trim die is installed in a trim press where the part is trimmed by atrim tool such as a steel rule die for simple flat cuts or a heaviersteel die for more complex shapes or for a higher volume of parts.

SUMMARY OF THE INVENTION

The present invention is directed to an improved thermoform toolingsystem which incorporates a trimming operation with the thermoform moldfor efficiently forming and trimming a sheet of heat deformable materialto form a molded part. The tooling system of the invention is ideallysuited for producing twin-sheet thermoformed parts, for example, asdisclosed in above-mentioned U.S. Pat. No. 5,813,355. The tooling systemalso eliminates the needs for additional molds, fixtures or trim dies totrim each part with a CNC router or with a separate trim press. Thusthere is no additional capital expenditure for a CNC router system or atrim press or for programming the CNC router. Also eliminated is therepair of damaged fixtures or the replacement of vacuum seals on trimfixtures, all of which cause a loss in production of parts. In addition,the thermoformed tooling system of the invention eliminates the need foran operator or operators to place a formed part manually onto a fixturefor a CNC router or onto a trim press and the possibility of injury tothe operator. The tooling system of the invention further reduces theoverall cycle time for producing finished parts by eliminating thesecondary operation of separately trimming each molded part.

In accordance with the invention, an upper press platen is positionedabove a lower press platen, and upper and lower mold members aresupported by the upper and lower platens with at least one of the moldmember defining a cavity according to the shape of the part. A lowertrim frame closely surrounds the lower mold member and is mounted on thelower platen, and the lower mold member is slidable vertically withinthe lower trim frame. An upper trim frame closely surrounds the uppermold member and is connected to the upper platen with the upper moldmember slidable vertically within the upper trim frame.

The upper trim frame and lower trim frame are positioned in opposingrelation for clamping therebetween a peripheral portion of a singleheated sheet or peripheral portions of heated twin sheets in response tomovement of the mold members from an open position to a closed position.The cavity is connected to a vacuum source to form the heated sheet intothe cavity. After a heated sheet is formed into the cavity and cooled ortwin sheets are formed and fused together and cooled to form a part, theupper and lower mold members move or shift downwardly as a unit withinthe upper and lower trim frames to shear the thermoformed part from theperipheral portion of the sheet(s) clamped between the trim frames.After the shearing or trimming operation, the mold members open so thatthe trimmed part may be conveniently removed from the mold members, andthe separated peripheral portion of one or both sheets may be removedfrom the trim frames.

Other features and advantages of the invention will be apparent from thefollowing description, the accompanying drawings and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical section of a thermoform tooling system constructedin accordance with the invention and showing the trim frames and moldmembers in an open position with twin vacuum-formed heated sheets on themold members;

FIG. 2 is a vertical section similar to FIG. 1 and showing the trimframes and mold members in a closed position for fusing the upper sheetto the lower sheet;

FIG. 3 is a vertical section similar to FIG. 2 and showing the fusedtwin sheets after the trimming operation;

FIG. 4 is a vertical section similar to FIG. 1 with the trim frames andmold members in the open position and the trimmed part and peripheralportions carried by the upper mold member;

FIG. 5 is a vertical section of the closed mold members, taken generallyon the line 5-5 of FIG. 2 and without sheets of thermoformable material;

FIG. 6 is a vertical section similar to FIG. 5 and taken generally onthe lines 6-6 of FIG. 3;

FIG. 7 is an enlarged fragmentary section of the tooling system in theopen position shown in FIG. 1;

FIG. 8 is an enlarged fragmentary section of the tooling system duringthe twin-sheet fusing operation shown in FIG. 2; and

FIG. 9 is an enlarged fragmentary section of the tooling system shown inFIG. 3 after the trimming operation.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

Referring to FIG. 1, a thermoform tooling system 20 includes an upperplaten 22 above a lower platen 24 which is supported by parallel spacedbeams 26. The upper platen 22 is connected, in a conventional manner, toa fluid actuated cylinder (now shown) of a press for movement between anopen position (FIG. 1) and a closed position (FIG. 2), and the platens22 and 24 are preferably formed of aluminum. The upper platen 22supports and carries an upper mold plate or member 30 secured to thebottom of a cooling plate 32, both of which are formed of aluminum. Theupper platen 22 also supports an aluminum upper trim frame 35 whichclosely surrounds the mold member 30 and cooling plate 32 and isslidable vertically relative to the mold member 30 and plate 32. Thetrim frame 35 is supported from the upper platen 22 by a series ofperipherally spaced bolts 38 (FIG. 1) which extend through block members41 mounted on the platen 22 and are threaded into the trim frame 35. Acompression spring 42 surrounds each bolt 38, and the springs normallybias the trim frame 35 downwardly relative to the upper platen 22 andmold members 30 and 32 to the home position shown in FIG. 1.

Referring to FIGS. 1 and 5, a set of peripherally spaced pins or rods 46are also connected to the upper trim frame 35, and each rod 46 extendsupwardly into a corresponding support block 47 secured to the top of theupper platen 22. The upper ends of the rods 46 are normally blocked by aset of laterally extending or horizontal blocking bars 49, and each bar49 extends through aligned openings within the support blocks 47 andintermediate support blocks 52. Each blocking bar 49 is supported forlaterally sliding movement within the support blocks 47 and 52 between ablocking position (FIGS. 1 & 5) blocking upward movement of the rods 46and a released position (FIG. 6) when the rods 46 are free to moveupwardly within corresponding cavities 54 within each blocking bar 49.Each blocking bar 49 is shifted laterally between its blocking andrelease positions by a corresponding fluid cylinder 56 (FIG. 5) eachhaving a piston rod 57 connected to a bracket 59 secured to the blockingbar 49. As shown in FIGS. 1, 5 and 6, the cooling plate 32 supportingthe mold plate 30 has a series of interconnected cooling passages 62through which a cooling fluid or water is pumped when required.

Referring to FIGS. 1 and 2, the lower platen 24 supports a lower coolingplate 68 and a lower mold member 70 which has a set of cavities 72according to the configuration of the part to be thermoformed in thetooling system 20. A series of vacuum passages 74 (FIG. 1) extend fromthe cavities 72 through the mold member 70 and cooling plate 68 and areconnected to a vacuum source. The cooling plate 68 and the mold member70 are normally biased upwardly from the lower platen 24 by a set ofspaced compression springs 78 each of which extends within verticallyaligned cavities formed within the cooling plate 68 and a pad 81 securedto the bottom of the lower platen 24. A bolt 83 extends verticallythrough each pad 81 and corresponding compression spring 78 and isthreaded into the cooling plate 68 to limit upward movement of thecooling plate 68 and mold member 70 relative to the lower platen 24.

The bottom surface of the cooling plate 68 has laterally spaced recesses86 which define therebetween laterally spaced pads 88. A set oflaterally extending and parallel spaced elongated blocking bars 92 aresupported by the lower platen 24 for longitudinally sliding movement,and each bar 92 has longitudinally spaced recesses or cavities 94. Eachblocking bar 92 is moved or shifted laterally or horizontally by acorresponding fluid cylinder 96 (FIG. 1) having a piston rod 97connected to an actuator bracket or block 99 projecting downwardly fromthe bar 92. When the piston rod 97 is retracted, the blocking bar 92 isin its normal blocking position (FIGS. 1 & 2) supporting the pads 88 onthe cooling plate 68. When the piston rod 97 is extended, the blockingbar 92 shifts laterally or horizontally to a non-blocking or releasedposition (FIG. 3) so that the cooling plate 68 and mold member 70 mayshift downwardly relative to the lower platen 24 against the bias of thecompression springs 78. As shown in FIG. 6, the lower cooling plate 68also has interconnected fluid cooling passages 102 through which acooling fluid or water is pumped at selected times.

The lower mold member 70 and cooling plate 68 are closely surrounded bya lower trim frame 104 mounted on the lower platen 24 and within whichthe mold member 70 and cooling plate 68 may slide vertically. Referringto the enlarged section view of FIG. 7, the bottom surface of thealuminum upper trim frame 35 has a peripherally extending recess ordownwardly facing groove 106 and supports a peripherally extending steelpinch strip or pad 108. The aluminum upper mold plate or member 30supports a peripherally extending steel wear frame 110. The lower trimframe 104 includes a steel top trim frame 112 having a peripherallyextending recess or groove 114 and supporting a peripherally extendingsteel pinch strip or pad 116. The steel trim frame 112 also has aperipherally extending contoured pinch surface or ridge 118.

In operation of the thermoforming system 20 for producing a thermoformedproduct or part, a heated vacuum formed upper sheet 125 (FIG. 1) of heatdeformable or thermoplastic material is carried by the upper mold plateor member 30, and a peripheral portion 128 of the sheet 125 includes aperipherally extending inverted U-shaped portion 131 (FIG. 7) whichprojects into the groove 106 to retain the sheet. While the heated sheet125 is shown as being substantially flat under the mold member 30, it isto be understood that the mold member 30 may have one or more cavities,and the heated sheet 125 would be vacuum-formed into the cavities. Avacuum-formed heated lower sheet 135 (FIGS. 1 & 7) of heat deformable orthermoplastic material is supported by the lower mold member 70 and isvacuum-formed into the cavities 72 within the lower mold member. Thelower sheet 135 has a peripheral portion 138 which extends over theridge 118 and into the groove 114 and over the pinch pad 116 of thesteel trim frame 112. The vacuum-formed sheets 125 and 135 are heated toa predetermined temperature, for example, about 400° F., for the vacuumforming process.

Referring to FIGS. 2 and 8, when it is desired to fuse the upper sheet125 to the lower sheet 135, the upper platen 22 is lowered by the pressuntil the peripheral portions 128 and 138 of the sheets are pinchedtogether by the trim frames 35 and 112, as shown in FIG. 2. In thisposition, the upper sheet 125 and lower sheet 135 are knitted or fusedtogether with heat and pressure and between the upper mold member 30 andlower mold member 70, and the peripheral portions 128 and 138 are fusedtogether as shown in FIG. 8. The fused together sheets cool to a lowertemperature, for example, within the range of 150° to 180°, preferablywith the aid of cooling fluid circulating within the passages 62 and 102and/or with the aid of circulating air fans directed against the platens22 and 24 and trim frames 35 and 104.

After the fusing operation, the upper blocking bars 49 and the lowerblocking bars 92 are then shifted laterally by the corresponding fluidcylinders 56 and 96. The upper platen 22, cooling plate 32 and uppermold member 30 are then shifted downwardly by a small amount within thetrim frame 35 (FIGS. 3 and 6), and the downward movement of the uppermold member 30 forces the lower mold member 70 and cooling plate 68downwardly against the compression spring 78. This downward movement ofthe upper mold plate 30 and lower mold plate 70 within the trim frames35 and 104 causes the steel trim frame 110 to cooperate with the steeltrim frame 112 to shear the fused sheets 125 and 135 from the fusedperipheral portions 128 and 138 of the sheets, as shown in FIG. 9, toproduce the thermoformed part P having a precise and clean outer edgesurface.

When the upper platen 22 and upper mold member 30 and cooling plate 32move upwardly and return to the normal open position (FIG. 4), thesprings 78 return the lower mold member 70 and cooling plate 68 back totheir upper home position, after which the blocking member 92 is shiftedto its blocking position by actuation of the cylinder 96. When the upperplaten 22 returns to its upper home position (FIG. 4), the springs 42shift the upper trim frame 35 downwardly on the upper mold member 30 andcooling plate 32 to the home position (FIG. 4). Each blocking bar 49 isthen returned to its blocking home position (FIG. 5) by actuation of thecorresponding cylinder 56. As shown in FIG. 4, the fused togethertrimmed sheets forming the part P are carried upwardly by the upper moldmember 30 along with the separated and fused together peripheralportions 128 and 138 of the sheets. In this position, the trimmed part Pand the peripheral edge portions may be conveniently removed from theupper mold member 30 and upper trim frame 35.

From the drawings and the above description, it is apparent that athermoform tooling system constructed in accordance with the invention,provides desirable features and advantages. As a primary advantage, aheated single sheet or heated twin sheets are completely thermoformedand trimmed in the tooling system, thereby eliminating the need for asecondary trimming station and operation at a remote site. As a result,the tooling system eliminates all of the problems of a secondarytrimming station and operation as described above in the Background ofthe Invention. In addition, the thermoforming and trimming operations inthe tooling system may be performed in substantially the same cycle timeas required to heat a sheet at a separate heating station, Usually, thetime period required for heating a sheet is the longest time period anddetermines the cycle time for operating a thermoforming apparatus suchas disclosed in above-mentioned U.S. Pat. No. 5,843,366.

While the method and form of thermoforming system or apparatus hereindescribed constitutes a preferred embodiment of the invention, it is tobe understood that the invention is not limited to the precise methodand form of apparatus described, and that changes may be made thereinwithout departing from the scope and spirit of the invention as definedin the appended claims.

1. A method of efficiently thermoforming and trimming a part from aheated first sheet of heat deformable material, comprising the steps offorming an upper mold member and a lower mold member with at least oneof the mold members defining a cavity therein, forming an upper trimframe closely surrounding the upper mold member and a lower trim frameclosely surrounding the lower mold member, supporting the upper moldmember and the upper trim frame with an upper platen with the upper moldmember slidable within the upper trim frame, supporting the lower moldmember and the lower trim frame with a lower platen and with the lowermold member slidable within the lower trim frame, locating the firstsheet of material between the upper mold member and the lower moldmember while the mold members are in an open position, moving the uppertrim frame and the lower trim frame together to clamp a peripheralportion of the first sheet between the upper trim frame and the lowertrim frame while moving the upper mold member and the lower mold membertogether to a close position, applying a suction within the cavity tothermoform the heated first sheet into the cavity while the peripheralportion of the first sheet is clamped between the trim frames to formthe part, sliding the upper mold member and the lower mold member as aclosed unit within the corresponding surrounding upper trim frame andthe lower trim frame to shear the peripheral portion of the first sheetfrom the part, and moving the upper trim frame and upper mold memberrelative to the lower trim frame and lower mold member to the openposition to provide for removing the trimmed part from the mold membersand removing the peripheral portion of the first sheet from the trimframes.
 2. A method as defined in claim 1 and including the step oflocating a second sheet of heat deformable material adjacent the firstsheet, fusing the first sheet and the second sheet together between theupper mold member and the lower mold member, and shearing peripheralportions of both the first and second sheets between the upper and lowertrim frames to form a twin sheet part.
 3. A method as defined in claim 2and including its step of blocking downward movement of the upper platenand upper mold member within the upper trim frame while fusing the firstsheet and second sheet together.
 4. A method as defined in claim 1 andincluding the step of blocking downward movement of the lower moldmember within the lower trim frame while the first sheet is thermoformedinto the cavity.
 5. A method of efficiently forming and trimming aheated sheet of heat deformable material to produce a molded part, saidmethod comprising the steps of forming a lower press platen and an upperpress platen with a lower mold member supported by the lower platen andan upper mold member supported by the upper platen and with at least oneof the mold members defining a cavity therein, connecting a lower trimframe to the lower platen with the lower trim frame closely surroundingthe lower mold member and with the lower mold member supported forsliding movement within the lower trim frame, connecting an upper trimframe to the upper platen with the upper trim frame closely surroundingthe upper mold member and with the upper mold member supported forsliding movement within the upper trim frame, positioning the upper trimframe and the lower trim frame in opposing relation for clampingtherebetween a peripheral portion of the heated sheet in response tomovement of the lower mold member and the upper mold member from an openposition to a closed position, extending at least one vacuum passage tothe cavity within the one mold member and connecting the passage to avacuum source to vacuum form the heated sheet into the cavity while themold members are in the closed position to form the molded part, movingthe upper mold member and the lower mold member as a unit within theupper trim frame and the lower trim frame while the mold members are inthe closed position to shear the molded part from the peripheral portionof the sheet clamped between the trim frames before the mold membersmove to the open position to release the molded part, and biasing theupper trim frame downwardly from the upper platen to a clamping positionwhile connecting the upper platen to the upper trim frame to permitdownward movement of the upper platen and the upper mold member withinthe upper trim frame.
 6. A method as defined in claim 5 and includingthe step of supporting a blocking member by the upper platen for lateralmovement between a blocking position preventing upward movement of theupper trim frame relative to the upper platen and a release positionpermitting the downward movement of the upper platen and the upper moldmember within the upper trim frame.
 7. A method of efficiently formingand trimming a heated sheet of heat deformable material to produce amolded part, said method comprising the steps of forming a lower pressplaten and an upper press platen with the upper press platen positionedabove the lower press platen, supporting a lower mold member by thelower platen and supporting an upper mold member by the upper platenwith at least one of the mold members defining a cavity therein,positioning a lower trim frame closely surrounding the lower mold memberwith the lower mold member supported for vertical sliding movementwithin the lower trim frame, positioning an upper trim frame closelysurrounding the upper mold member with the upper mold member supportedfor vertical sliding movement within the upper trim frame, positioningthe upper trim frame and the lower trim frame in opposing relation forclamping therebetween a peripheral portion of the heated sheet inresponse to movement of the lower mold member and the upper mold memberfrom an open position to a closed position, extending a vacuum passageto the cavity within the one mold member and connecting the passage to avacuum source to vacuum form the heated sheet into the cavity while themold members are in the closed position to form the molded part, movingthe upper mold member and the lower mold member as a unit within theupper trim frame and within the lower trim frame to a trim positionwhile the mold members are in the closed position to shear the moldedpart from the peripheral portion of the sheet clamped between the trimframes before the mold members move to the open position to release themolded part, biasing the lower mold member upwardly from the lowerplaten to a molding position, and biasing the upper trim framedownwardly from the upper platen to a clamping position.
 8. A method asdefined in claim 7 and including the steps of blocking downward movementof the lower mold member from the molding position, and releasing theblocking to permit downward movement of the lower mold member toward thelower platen.
 9. A method as defined in claim 7 including the steps ofblocking upward movement of the upper trim frame relative to the upperplaten, and releasing the blocking to permit downward movement of theupper mold member from the upper platen.
 10. A method as defined inclaim 7 and including the steps of positioning a second heated sheet ofheat deformable material adjacent the first said sheet of material toform twin sheets of material, fusing the twin sheets together betweenthe upper mold member and the lower mold member before the mold membersare movable as a unit within the upper trim frame and the lower trimframe to the trim position.
 11. A method as defined in claim 7 andincluding the steps of supporting at least one blocking member by thelower platen for lateral movement between a first position blockingdownward movement of the lower mold member from the molding position anda second position allowing downward movement of the lower mold member,and supporting at least one blocking member by the upper platen forlateral movement between a blocking position preventing upward movementof the upper trim frame relative to the upper platen and a releaseposition permitting downward movement of the upper platen and the uppermold member within the upper trim frame.